This invention relates to web coating apparatus of the sort in which coating material is supplied to a coater head (usually having a doctor blade) for application to a moving web supported on a backup roll. The body of the head provides the rear wall and floor of a coating chamber, and dikes are provided to close the ends of the chamber and seal against the backup roll. Typically the dikes will seal against the margins of the web, preventing the coating from rolling over to the other side of the web; in such cases the web will have uncoated margins, which are usually trimmed.
In a copending U.S. patent application, Ser. No. 646,527, now abandoned, entitled COATING WEBS, filed on the same day as this application by F. Peter Ford, there is disclosed and claimed Mr. Ford's invention of a dike system comprising a pair of inboard dikes spaced along the backup member axis, each inboard dike having a control surface shaped to conform to the backup member along a margin of the web and having an operating position in which the control surface is spaced from the backup member sufficiently to allow the coating material to bleed between the control surface and the web to coat the margin, the control surface in the operating position being sufficiently close to the backup member to confine most of the coating material to between the inboard dikes, and a pair of outboard dikes respectively spaced outwardly from the inboard dikes along the axis, the outboard dikes each having a sealing surface and an operation position in which the sealing surface is in sealing contact with the backup member to prevent leakage of the coating material bleeding past the inboard dikes, the head being provided with drainage openings for draining the coating material from the zones between the inboard and outboard dikes.